Only when you decide to build your own runtime API for Blaze to replaces Spacebars with something else such as Jade or Markdown you will need to familiarize yourself with the internal processing structures.

I think you mean to say:

Only when you decide to build your own runtime API for Blaze, replacing Spacebars with something else such as Jade or Markdown, will you need to familiarize yourself with the internal processing structures.